In this doctoral thesis, Kant's distinction between perfect and imperfect duties is examined. The thesis begins with an exploration of how the distinction originates and evolves in the writings of three of Kant's most prominent natural law predecessors: Hugo Grotius, Samuel von Pufendorf, and Christian Wolff. The thesis then moves on to Kant's own writings. It is argued that Kant draws the perfect-imperfect distinction in as many as twelve different ways, that these ways are not entirely consistent with one another, and that many of them, even taken by themselves, do not hold up to scrutiny. Furthermore, it is argued that Kant's claim that perfect duties always trump imperfect duties - which can be referred to as "the priority claim" - is not actually supported by any one of the ways in which Kant draws the perfect-imperfect distinction. After this critical reading of Kant's writings, the thesis then switches gears and a more "positive" project is attempted. It is argued that the perfect-imperfect distinction, even though it does not support the priority claim, is not altogether normatively neutral or uninteresting. In particular, for some of the ways in which the distinction is drawn, it is shown that the distinction yields the following normative implication: Sometimes perfect duties override imperfect duties and all other times there is no priority one way or the other. Finally, it is explained that this normative implication - which can be referred to as the "privilege claim" - translates into the following practical directive: When there is a conflict between a perfect duty and an imperfect duty, sometimes one must act in conformity with the former duty and all other times one is free to choose which of the two duties to act in conformity with. This practical directive represents the ultimate finding of this thesis.